Low bend loss optical fiber

ABSTRACT

One embodiment of a single mode optical fiber includes:
         a graded index central core region having outer radius r 1  and relative refractive index Δ 1 ;   a cladding region comprising (i) a first inner cladding region having an outer radius r 2 &lt;10 microns and relative refractive index Δ 2  and 0.65≦r 1 /r 2 ≦1; (ii) and a second inner cladding region (i.e., trench) having an outer radius r 3 &gt;10 microns and comprising a minimum relative refractive index Δ 3 , wherein said second inner cladding region has at least one region with a relative refractive index delta that becomes more negative with increasing radius; and (iii) an outer cladding region surrounding the second inner cladding region and comprising relative refractive index Δ 4 , wherein Δ 1 &gt;Δ 2 &gt;Δ 3 , Δ 3 &lt;Δ 4 .

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. patent applicationSer. No. 13/485,028 filed on May 31, 2012 the content of which is reliedupon and incorporated by reference in its entirety, and the benefit ofpriority under 35 U.S.C. §120 is hereby claimed. This application alsoclaims the benefit of priority under 35 U.S.C. §119 of U.S. ProvisionalApplication Ser. No. 61/564,902 filed on Nov. 30, 2011 the content ofwhich is relied upon and incorporated herein by reference in itsentirety.

FIELD

The present invention relates to optical fibers having low bend losses.

TECHNICAL BACKGROUND

There is a need for low bend loss optical fibers, particularly foroptical fibers utilized in so-called “access” and fiber to the premises(FTTx) optical networks. Optical fiber can be deployed in such networksin a manner which induces bend losses in optical signals transmittedthrough the optical fiber. Some applications or optical components thatutilize optical fiber can impose physical demands, such as tight bendradii, compression of optical fiber, etc., that induce bend losses.These applications and/or components include the deployment of opticalfiber in optical drop cable assemblies, distribution cables with FactoryInstalled Termination Systems (FITS) and slack loops, small bend radiusmultiports located in cabinets that connect feeder and distributioncables, and jumpers in Network Access Points between distribution anddrop cables. It has been difficult in some single mode optical fiberdesigns to achieve low bend loss at 1550 nm at both small and large benddiameters.

SUMMARY

According to some embodiments a single mode optical fiber includes:

a graded index central core region having outer radius r₁, having arelative refractive index Δ₁, a maximum relative refractive indexΔ_(1max) and having an alpha profile, alpha_(core), of0.5≦alpha_(core)≦4;

a cladding region including

-   -   (a) a trench region surrounding said graded index central core        region and comprising a relative refractive index delta Δ₃ that        becomes more negative with increasing radius, said trench region        having an inner radius r₂, an outer radius r₃>10 microns, and a        minimum relative refractive index Δ_(3min) such that        Δ_(1max)>Δ_(3min), r₃≧r_(3a), and 0.5≦(r_(3a)−r₂)/(r₃−r₂)≦1,        where r_(3a) is a distance from fiber centerline where Δ₃ first        reaches the value Δ_(3min), said trench region having an alpha        profile, alpha_(t) such that 0.5≦alpha_(t)≦5, and    -   (b) an outer cladding region surrounding said trench region and        having a relative refractive index Δ₄, and Δ_(3min)<Δ₄.

In at least some embodiments the single mode optical fiber furthercomprises a first inner cladding region situated between the gradedindex central core region and the trench region (i.e. between gradedindex central core region and the second inner cladding region that hasa relative refractive index delta that becomes more negative with theincreasing radius).

According to some embodiments a single mode optical fiber includes:

a graded index germania doped central core region having outer radiusr₁, having a relative refractive index Δ₁, a maximum relative refractiveindex Δ_(1max) and having an alpha profile, alpha_(core), of0.5≦alpha_(core)≦4;

a cladding region comprising (i) a first inner cladding region having anouter radius r₂≦10 microns and relative refractive index Δ₂ and0.65≦r₁/r₂<1; (ii) and a second inner cladding region having an outerradius r₃>10 microns and comprising a relative refractive index Δ₃ and aminimum relative refractive index Δ_(3min), wherein said second innercladding region has a relative refractive index delta that becomes morenegative with increasing radius, wherein the second inner claddingregion has an alpha profile, alpha_(t), of 0.5≦alpha_(t)≦5; (iii) anouter cladding region surrounding the second inner cladding region andcomprising relative refractive index Δ₄, wherein Δ_(1max)>Δ₂>Δ_(3min),and Δ_(3min)<Δ₄; and wherein 0.5≦(r_(3a)−r₂)/(r₃−r₂)≦1.

According to some embodiments disclosed herein an optical fibercomprises a graded central core region having outer radius r₁ and amaximum relative refractive index delta Δ_(1max), a cladding comprisinga first inner cladding region having an outer radius r₂ such thatr₁≦r₂<8 microns and a relative refractive index delta Δ₂, a second innercladding region having a relative refractive index delta Δ₃ and aminimum relative refractive index delta Δ_(3min), whereinΔ₁>Δ₂>Δ_(3min), such that the difference between Δ₂ and Δ_(3min) isgreater than 0.08%, and an outer cladding region surrounding the twoinner cladding regions. The fibers embodiments disclosed hereinpreferably exhibit a 22 m cable cutoff less than or equal to 1260 nm, amode field diameter (MFD) at 1310 nm between 8.2 and 9.6 microns and azero wavelength dispersion wavelength between 1300 and 1324 nm. In atleast some fibers embodiments r₁/r₂ is greater than or equal to 0.6,more preferably greater than 0.65, and less than or equal to 1. In atleast some fibers embodiments r₁/r₂ is greater than or equal to 0.75,more preferably greater than 0.8 and less than or equal to 1.

According to some other embodiments a single mode optical fiberincludes:

a graded index germania doped central core region having outer radiusr₁, peak (maximum) relative refractive index delta in the central coreregion of Δ_(1max); and the core region having a graded index alphaprofile with alpha_(core) between 1 and 3;

a cladding region comprising (i) a first inner cladding region having anouter radius 4.5 microns<r₂<9 microns and relative refractive index Δ₂and 0.65≦r₁/r₂≦1; (ii) and a second inner cladding region having anouter radius r₃>10 microns and comprising a minimum relative refractiveindex delta Δ_(3min), wherein said second inner cladding region has atleast one region with a relative refractive index delta that becomesmore negative with increasing radius wherein said second inner claddingregion has an alpha profile, alpha_(t), of 0.5≦alpha_(t)≦5; and (iii) anouter cladding region surrounding the inner cladding region andcomprising relative refractive index Δ₄, wherein Δ₁>Δ₂>Δ_(3min),Δ_(3min)<Δ₄.

Also disclosed herein are optical fiber embodiments comprising a centralcore region having outer radius r₁ and a maximum relative refractiveindex delta Δ_(1max), a cladding region comprising a first innercladding region having an outer radius r₂<8 microns and a relativerefractive index delta Δ₂, and a second inner cladding regionsurrounding the first inner cladding region and having relativerefractive index Δ₃, wherein Δ_(1max)>Δ₂>Δ_(3min), and Δ₂−Δ_(3 min) is≧0.1. The fibers disclosed herein preferably exhibit a 22 m cable cutoffless than or equal to 1260 nm, mode field diameter (MFD) at 1310 nmbetween 8.2 and 9.6 microns and zero wavelength dispersion between 1300and 1324 nm. In these fibers some embodiments r₁/r₂ is greater than orequal to 0.6, more preferably between 0.8 and 1. Preferably,|Δ₄−Δ₂|≧0.01.

Applicants have discovered that having a fiber with a trench that has anon-constant relative refractive index delta helps in achieving goodmacrobending performance at both small (<10 mm) and large (>20 mm)diameters. The following single mode fiber embodiments have a trenchwith a non-constant relative refractive index delta that decreases withan increasing radius in at least a region thereof, resulting in lowmacrobend loss and opticals (optical performance parameters) that areITU-G.652 standards compliant. In at least some embodiments the index inthe second inner cladding region decreases with increasing radialposition.

In at least some embodiments α_(t)≦5, where α_(t) (i.e., alpha_(t)) is atrench alpha parameter. For some embodiments 0.5≦α_(t)≦5.

Reference will now be made in detail to the present preferredembodiments, examples of which are illustrated in the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-6 show schematic relative refractive index profilescorresponding to several embodiments of an optical fiber as disclosedherein.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Additional features and advantages will be set forth in the detaileddescription which follows and will be apparent to those skilled in theart from the description or recognized by practicing as described in thefollowing description together with the claims and appended drawings.

The “refractive index profile” is the relationship between refractiveindex or relative refractive index and optical fiber radius. The radiusfor each segment of the refractive index profile is given by theabbreviations r₁, r₂, r₃, r₄, etc. and lower an upper case are usedinterchangeability herein (e.g., r₁ is equivalent to R₁).

The “relative refractive index percent” is defined as Δ %=100×(n_(i)²−n_(c) ²)/2n_(i) ², and as used herein n_(c) is the refractive index ofthe outer cladding region and unless otherwise specified is therefractive index of pure silica As used herein, the relative refractiveindex is represented by Δ and its values are given in units of “%”,unless otherwise specified. The terms: relative refractive index delta,delta, Δ, Δ %, %Δ, delta %, % delta and percent delta may be usedinterchangeability herein. In cases where the refractive index of aregion is less than the average refractive index of the outer cladding,the relative index percent is negative and is referred to as having adepressed region or depressed index. In cases where the refractive indexof a region is greater than the average refractive index of the outercladding region, the relative index percent is positive. An “updopant”is herein considered to be a dopant which has a propensity to raise therefractive index relative to pure undoped SiO₂. A “downdopant” is hereinconsidered to be a dopant which has a propensity to lower the refractiveindex relative to pure undoped SiO₂. Examples of updopants include GeO₂(germania), Al₂O₃, P₂O₅, TiO₂, Cl, Br. Examples of down dopants includefluorine, boron and non-periodic voids. The terms alpha_(core),alpha_(c) and α(core) refer to the core alpha and are usedinterchangeably herein. For a person skilled in the art, it will beobvious that the relative index profiles disclosed herein can bemodified such that entire index profile is shifted linearly up or downrelative to the index of pure silica and result in similar opticalproperties of the resulting optical fibers.

“Chromatic dispersion”, herein referred to as “dispersion” unlessotherwise noted, of an optical fiber is the sum of the materialdispersion, and the waveguide dispersion. Zero dispersion wavelength isa wavelength at which the dispersion has a value of zero. Dispersionslope is the rate of change of dispersion with respect to wavelength.

“Effective area” is defined in equation 1 as:A _(eff)=2π(∫f ² rdr)²/(∫f ⁴ rdr)  (Eq. 1)where the integration limits are 0 to ∞, and f is the transversecomponent of the electric field associated with light propagated in thewaveguide. As used herein, “effective area” or “A_(eff)” refers tooptical effective area of the optical fiber, at a wavelength of 1550 nmunless otherwise noted.

The term “α-profile” refers to a relative refractive index profile ofthe region, expressed in terms of Δ(r) which is in units of “%”, where ris radius, which for the core alpha follows the equation 2,Δ(r)=Δ(r _(o))(1−[|r−r _(o)|/(r ₁ −r _(o))]^(α(core)))  (Eq. 2)where r_(o) is the point at which Δ(r) is maximum, r₁ is the point atwhich Δ(r) % is zero, and r is in the range r_(i)≦r≦r_(f), where Δ isdefined above, r_(i) is the initial point of the α-profile, r_(f) is thefinal point of the α-profile, and α is an exponent which is a realnumber.

The mode field diameter (MFD) is measured using the Peterman II methodas shown in equations 3 and 4, respectively wherein,2w=MFD  (Eq. 3)andw ²=(2∫f ² rdr/∫[df/dr] ² rdr)  (Eq. 4)

wherein the integral limits being 0 to ∞.

The bend resistance of an optical fiber can be gauged by inducedattenuation under prescribed test conditions, for example by deployingor wrapping the fiber around a mandrel of a prescribed diameter, e.g.,by wrapping 1 turn around a either a 6 mm, 10 mm, 20 mm, 30 mm orsimilar diameter mandrel (e.g. “1×10 mm diameter macrobend loss” or the“1×30 mm diameter macrobend loss”) and measuring the increase inattenuation per turn.

One type of bend test is the lateral load microbend test. In thisso-called “lateral load wire mesh” test (LLWM), a prescribed length ofoptical fiber is placed between two flat plates. A #70 wire mesh isattached to one of the plates. A known length of optical fiber issandwiched between the plates and a reference attenuation is measuredwhile the plates are pressed together with a force of 30 Newtons. A 70Newton force is then applied to the plates and the increase inattenuation in dB/m is measured. The increase in attenuation is thelateral load attenuation of the optical fiber in dB/m at a specifiedwavelength (typically within the range of 1200-1700 nm, e.g., 1310 nm or1550 nm or 1625 nm).

The “pin array” bend test is used to compare relative resistance ofoptical fiber to bending. To perform this test, attenuation loss ismeasured for an optical fiber with essentially no induced bending loss.The optical fiber is then woven about the pin array and attenuationagain measured. The loss induced by bending is the difference betweenthe two measured attenuations. The pin array is a set of ten cylindricalpins arranged in a single row and held in a fixed vertical position on aflat surface. The pin spacing is 5 mm, center to center. The pindiameter is 0.67 mm During testing, sufficient tension is applied tomake the optical fiber conform to a portion of the pin surface. Theincrease in attenuation is the pin array attenuation in dB of theoptical fiber at a specified wavelength (typically with in the range of1200-1700 nm, e.g., 1310 nm or 1550 nm or 1625 nm).

The theoretical fiber cutoff wavelength, or “theoretical fiber cutoff”,or “theoretical cutoff”, for a given mode, is the wavelength above whichguided light cannot propagate in that mode. A mathematical definitioncan be found in Single Mode Fiber Optics, Jeunhomme, pp. 39-44, MarcelDekker, New York, 1990 wherein the theoretical fiber cutoff is describedas the wavelength at which the mode propagation constant becomes equalto the plane wave propagation constant in the outer cladding. Thistheoretical wavelength is appropriate for an infinitely long, perfectlystraight fiber that has no diameter variations.

Fiber cutoff is measured by the standard 2 m fiber cutoff test, FOTP-80(EIA-TIA-455-80), to yield the “fiber cutoff wavelength”, also known asthe “2 m fiber cutoff” or “measured cutoff”. The FOTP-80 standard testis performed to either strip out the higher order modes using acontrolled amount of bending, or to normalize the spectral response ofthe fiber to that of a multimode fiber.

By cabled cutoff wavelength, or “cabled cutoff” as used herein, we meanthe 22 m cabled cutoff test described in the EIA-445 Fiber Optic TestProcedures, which are part of the EIA-TIA Fiber Optics Standards, thatis, the Electronics Industry Alliance-Telecommunications IndustryAssociation Fiber Optics Standards.

Unless otherwise noted herein, optical properties (such as dispersion,dispersion slope, etc.) are reported for the LP01 mode.

Applicants discovered that putting an off-set trench with a non-constantdepth in the profile of a single mode fiber can simultaneously improvebend performance at both small (≦10 mm) and large (≧20 mm) benddiameters. The following fiber embodiments result in low bendperformance at small and large bend diameters and have other opticalsthat are G.652 standards compliant (MFD between 8.2 and 9.6 microns at1310 nm, zero dispersion wavelength between 1300 and 1324 nm, cablecutoff wavelength less than or equal to 1260 nm).

Preferably MFD (at a wavelength of 1310 nm) of the optical fiber 10 isbetween 8.2 microns and 9.6 microns. For example, 8.2 microns≦MFD≦and9.6 microns, or 8.5 microns≦MFD≦and 9.4 microns (e.g., 8.6 microns, 8.8microns, 9 microns, 9.2 microns, 9.4 microns, 9.6 microns, ortherebetween).

As shown in FIGS. 1-6, according to some embodiments a single modeoptical fiber 10 includes:

a graded index central core region 1 (or core) having outer radius r₁,having a relative refractive index Δ₁, a maximum relative refractiveindex Δ_(1max) and having an alpha profile, alpha_(core), of0.5≦alpha_(core)≦4; and a cladding region surrounds the core andcomprises at least one inner cladding region 2, 3 and an outer claddingregion 4. The second inner cladding region 3 (also referred to as atrench, trench region, or moat herein) has an inner radius r₂ and anouter radius r₃. In some embodiments r₃>10 microns. Region 3 alsocomprises a relative refractive index Δ₃ and a minimum relativerefractive index Δ_(3min), such that its relative refractive index deltabecomes more negative with increasing radius. The inner cladding region3 has an alpha profile, alpha_(t), and preferably 0.5≦alpha_(t)≦5. Theouter cladding region 4 surrounds the inner cladding region and has arelative refractive index Δ₄, wherein Δ_(1max)>Δ₂>Δ_(3min), andΔ_(3min)<Δ₄. In the optical fiber embodiments of FIGS. 1-6 r₁≦r₂. Insome preferred embodiments 0.65≦r₁/r₂≦1.

According to some embodiments optical fiber 10 includes a first innercladding region 2 with an outer radius r₂, and a second inner claddingregion 3 with an outer radius r₃. For these embodiments r₁<r₂. In someembodiments, the optical fiber 10 does not include the first innercladding region 2 (see FIG. 4, for example), for these embodiments r₂=r₁and the ratio r₁/r₂=1.

Several schematic refractive index profiles of an exemplary fiber 10 areshown in FIGS. 1-6. Optical fibers 10 of FIGS. 1-6 include a centralgraded index glass core region 1 (or core) comprising maximum relativerefractive index delta percent Δ_(1max). The core region 1 has a gradedindex profile also referred to as a gradient or graded index profileherein. Optical fibers 10 may have core regions with the alpha_(core)values (α_(core)) ranging as 0.5≦α_(core)≦5, in some embodiments1≦α_(core)≦5, in some embodiments 1≦α_(core)≦4, in some embodiments1.5≦α_(core)≦3 in some other embodiments 1.5≦α_(core)≦2.5. As shown inFIGS. 1-3 and 5-6, in some embodiments of the optical fiber 10 thesecond inner cladding region 3 is offset from the core region 1, suchthat the optional first inner cladding region 2 is sandwiched betweenthe central glass core region 1 and the second inner cladding region 3(in these embodiments r₂>r₁). The outer cladding region 4 surrounds thesecond inner cladding region 3 and comprises a relative refractive indexdelta 44. In these embodiments the first, optional, inner claddingregion 2 surrounds and is directly adjacent to the central core region1, and comprises a relative refractive index delta percent Δ₂. In theseembodiments the second inner cladding region 3 surrounds the first innercladding region 2 and comprises refractive minimum index delta percentΔ_(3min). In the fiber embodiments that do not include the first innercladding region 2 (as shown for example in FIG. 4) the second innercladding region 3 (i.e., the trench region) surrounds and is directlyadjacent to the core region 1, the second inner cladding region 3comprising minimum relative refractive index delta percent Δ_(3min). Inthese embodiments, for modeling purposes, we set r₂=r₁, and Δ₂=Δ_(3max).

The second inner cladding region 3 does not have a constant Δ₃(r).Preferably Δ₃(r) decreases with increasing radius and may have atriangular cross-section. Thus, in some embodiments minimum relativerefractive index Δ₃ of this region occurs at r=r₃ (i.e.,Δ₃(r=r₃)=Δ_(3min)). Preferably the second inner cladding region 3comprises silica doped with fluorine. The outer cladding region 4surrounds second inner cladding region 3 (i.e., the trench) andcomprises relative refractive index delta percent Δ₄

FIG. 1 illustrates a relative refractive index profile Δ₃(r) of anembodiment of fiber 10 that has a triangular trench profile. This figureshows that the relative refractive index of the second inner claddingregion 3 monotonically decreases with increasing radius, andΔ₃(r₂)>Δ₃(r₃). In the embodiment of FIG. 1 Δ₂=Δ₄. However, Δ₂ does notneed to be the same as Δ₄ (e.g., Δ₂ may be larger or smaller than 44. Insome embodiments, Δ₄≦Δ₂. In some embodiments, 0.00%≦(Δ₄−Δ₂)≦0.1%.

FIG. 2 illustrates a relative refractive index profile of embodiment offiber 10 that has a trapezoid-shaped trench profile. In this embodimentthe relative refractive index of the second inner cladding region 3 alsodecreases with increasing radius, and Δ₃(r₂)>Δ₃(r₃). In the embodimentof FIG. 2 Δ₂=Δ₄, but in some embodiments Δ₂ and Δ₄ have different values(e.g., Δ₂>Δ₄, or Δ₂<Δ₄).

FIG. 3 illustrates a relative refractive index profile of anotherembodiment of fiber 10. In this embodiment the relative refractive indexof the second inner cladding region 3 monotonically decreases withincreasing radius until it reaches a value r=r_(3a), and then isconstant between the radii r_(3a) and r₃. In this embodimentΔ₃(r₂)>Δ₃(r₃) and Δ₃(r₂)>Δr₃(r_(3a)). As shown in FIG. 3, for example,radius r_(3a) is the radius where the value Δ_(3min) is first reached,moving radially outward from the centerline. In some embodiments,r_(3a)=r₃. (See, for example, FIGS. 1, 2, 4 and 5) In the embodimentshown in FIG. 3 Δ₂=Δ₄ but in some embodiments Δ₂ and Δ₄ have differentvalues (e.g., Δ₂>Δ₄, or Δ₂<Δ₄). In some embodiments 0.1%≧|Δ₂−Δ₄|≧0.01%.

FIG. 4 illustrates relative refractive index profile of an embodiment offiber 10 that also has a trench profile that is similar to the profileof FIG. 1, but in FIG. 4 the width of the first inner cladding region 2is zero, i.e., this fiber embodiment does not have the inner claddingregion 2. In this embodiment r₁=r₂.

FIG. 5 illustrates relative refractive index profile of an embodiment offiber 10 that also has a trench profile that is similar to the profileof FIG. 1, but in FIG. 5 the relative refractive index profile of thesecond inner cladding region 3 has a shape that is concave.

FIG. 6 illustrates relative refractive index profile of an embodiment offiber 10 that also has a trench profile and that is similar to theprofile of FIG. 1, but in FIG. 6 the relative refractive index profileof the second inner cladding region 3 has a convex portion. That is, therelative refractive index of the of the second inner cladding region 3decreases relatively slowly in a region close to the first innercladding region 2 and then relatively rapidly as the radius approachesr₃ (in a region of the second inner cladding region 3 that is closer tothe outer cladding region).

In the exemplary embodiments, Δ_(1max)>Δ₂>Δ_(3min) and Δ_(3min)<Δ₄.Preferably Δ₂−Δ_(3min)≧0.08%. In some embodiments0.08%≦Δ₂−Δ_(3min)≦0.7%. In other embodiments 0.08%≦Δ₂−Δ_(3min)≦0.25%. Inother embodiments 0.25%≦Δ₂−Δ_(3min)≦0.55%. Additional optional core orcladding regions may be employed. For example (not shown), anotherregion (2A) may be situated between the core and the region 3. Theoptional inner cladding region 2A may be may be directly adjacent to andsurround core region 1 and comprise a higher or a lower relativerefractive index delta percent Δ_(2A) than that of the annular region 2(i.e., Δ_(2A)<Δ₂, or Δ_(2A)>Δ₂). The index of refraction (and thus therelative refractive index delta) of the second inner cladding region 3(the trench region) preferably decreases with increasing radialposition.

Another parameter that can be used to define the trench shape (i.e., therefractive index shape of the second inner cladding region 3, wherer₂≦r≦r₃) is the parameter, α_(t) (alpha_(t)), which defines a relativerefractive index profile in the second inner cladding region 3,expressed in terms of Δ(r) which is in units of “%”, where r is radius,which follows the equation 5,Δ(r)=(Δ_(3min)−Δ(r ₂))(1−[|r ₃ −r|/(r ₃ −r ₂)]^(α) ^(t) )+Δ(r ₂)  (Eq.5)where α_(t) is the trench alpha parameter (also referred to as alpha_(t)herein). For a rectangular trench, the value of parameter α_(t) isgreater than 100, while for a triangular trench the value of parameterα_(t) is 1. Preferably α_(t)≦10. In some embodiments of optical fiber10, the parameter α_(t) is between 0.5 and 5, more preferably between0.5 and 3 and even more preferably between 0.75 and 2.

Central core region 1 comprises an outer radius r₁ which is defined asthe first radial location moving away radially outward from the Δ_(1max)corresponding to where a tangent line drawn through the maximum absoluteslope of the relative refractive index of central core region 1 (that isr=r₁ where |dΔ(r)/dr| is maximum) crosses the zero delta line. Coreregion 1 (also referred to as a core herein) preferably exhibits amaximum relative refractive index delta percent, Δ_(1max), between about0.3 to 0.5, more preferably between about 0.31 to 0.48, for examplebetween about 0.31 to 0.45. In some embodiments, Δ_(1max) is between0.31 and 0.43. In some embodiments Δ_(1max) is less than 0.42. Coreradius r₁ is preferably between 3 and 9 microns, more preferably betweenabout 3.5 to 8.0 microns, for example 3.5≦r₁≦7.0 microns, or 4.5≦r₁≦6.5microns. Central core region 1 may comprise a single segment, step indexprofile. In some embodiments, central core region 1 exhibits an alphaprofile with an alpha α value greater than 0.5 and less than 10, and insome embodiments less than 7.5, less than 5, or less than 3. In somepreferred embodiments, central core region 1 exhibits an alpha greaterthan 0.5 and less than 10, and in some embodiments less than 5, or lessthan 3, and a core region 1 having a relative refractive index deltapercent, Δ_(1max) between 0.30 to 0.48 (e.g., 0.36≦Δ₁≦0.44).

In the embodiment illustrated in FIG. 1, the inner cladding region 2surrounds central core region 1 and comprises inner radius r₁ and outerradius r₂, r₁ being defined as above and r₂ which is defined as thefirst radial location moving away radially outward from r₁ where therelative refractive index is equal to 0.03(Δ_(3min)). In some cases therelative refractive index in region 2 is essentially flat, in othercases there can be a gradient index profile, and in some embodimentsregion 2 decreases in relative refractive index as radius increases.Still in other cases there can be fluctuations as a result of smallprofile design or process variations. In some embodiments, the firstinner cladding region 2 contains less than 0.02 wt % fluorine. In someembodiments, the inner cladding region 2 comprises silica which issubstantially undoped with either fluorine or germania, i.e., such thatthe region is essentially free of fluorine and germania. In some otherembodiments, region 2 is doped with fluorine that is less than 0.2 wt %.According to some embodiments, the inner cladding region 2 exhibits awidth between about 0.2 to 6 microns, more preferably 0.5 to 5 microns,even more preferably between about 1 to 4 microns. Preferably, 5micron≦r₂≦9 micron, more preferably 6 micron≦r₂≦8 micron. The ratio ofthe core radius r₁ over the inner cladding region 2 radius r₂ ispreferably at least 0.75 and less than 1, more preferably greater than0.8.

Inner cladding region 2 comprises relative refractive index deltapercent Δ₂ which, when r₂ is not equal to r₁, is calculated usingequation 6:

$\begin{matrix}{\Delta_{2} = {\int_{r\; 1}^{r\; 2}{{\Delta(r)}\ {{\mathbb{d}r}/\left( {r_{2} - r_{1}} \right)}}}} & \left( {{Eq}.\mspace{14mu} 6} \right)\end{matrix}$

In some embodiments, the first inner cladding region 2 comprises silicawhich is substantially undoped with either fluorine or germania, i.e.,such that the region is essentially free of fluorine and germania. Innercladding region 3 preferably includes a down-dopant, for examplefluorine to provide a minimum relative refractive index delta that islower than that of region 2. In the embodiments illustrated in FIGS. 1-3and 5-6, the second inner cladding region 3 surrounds the first innercladding region 2 and comprises inner radius r₂ and outer radius r₃, r₂being defined as above and r₃ being defined as where the relativerefractive index profile curve again crosses the zero delta line (Δ₄) atthe first radial location moving away radially outward from the radiusr₂. (Please note that in the embodiment of FIG. 4, there is no innercladding, i.e., the inner cladding width is zero (r₁=r₂), in this caseΔ₂=Δ₃ max. In some cases the relative refractive index in region 3(i.e., the relative refractive index of the trench) can have a gradientindex profile, in some preferred embodiments the relative refractiveindex in region 3 has a shallower depression in the inner part of theregion and a deeper depression in the outer part of the region. Inaddition, there can be fluctuations as a result of small profile designor process variations In some embodiments the second inner claddingregion 3 includes fluorine and/or boron. Inner cladding region 3comprises relative refractive index delta percent Δ₃ (r), and theminimum relative refractive index delta Δ_(3min). The minimum index inthe second inner cladding region Δ_(3min) is preferably less than orequal to −0.08% (i.e., Δ₄−Δ₃≧0.08%). In some embodiments, Δ_(3min) lessthan or equal to −0.2%. In some embodiments, Δ_(3min) less than or equalto −0.35%. R₄ is the outer radial location of the optical fiber and isin the preferred range of 50 microns≦r₄≦75 microns, more preferably r₄is 62.5 microns.

The volume V_(3a3) of the second inner cladding region 3 (i.e., thevolume of the trench), is defined as shown in equation 7, and given inunits of percent delta micron² (%Δ microns²)

$\begin{matrix}{V_{3a\; 3} = {2{\int_{r\; 2}^{r\; 3}{{\Delta_{({4 - 3})}(r)}r\ {\mathbb{d}r}}}}} & \left( {{Eq}.\mspace{14mu} 7} \right)\end{matrix}$where Δ₍₄₋₃₎ is the index difference of (Δ₄−Δ₃). In the embodiments ofFIGS. 1-5 the absolute volume V_(3a3) of the inner cladding region 3 is5 Δ % microns²≦V_(3a3)≦105 Δ % microns². In some embodiments, morepreferably 5 Δ % microns²≦V_(3a3)≦75 Δ % microns². The inner claddingregion 3 preferably exhibits a width W₃, (r₃−r₂), between about 5 to 20microns, more preferably 5 to 15 microns. The ratio of the radius r₃over the inner cladding region 2 radius r₂ is preferably greater than1.3, more preferably between 1.5 and about 4. The moat volume ratio,V_(3a3ratio), is defined in equation 8 as follows, and given in units ofpercent delta micron² (%Δ microns²)V _(3a3ratio) =V _(3a3)/[Δ_(3min)(r ₃ ² −r ₂ ²)]  (Eq. 8)Preferably the optical fibers herein have a moat volume ratio of0.3≦V_(3a3ratio)≦0.8.

Outer cladding region 4 surrounds the depressed annular region 3 andcomprises relative refractive index delta percent Δ₄ which is higherthan the index Δ_(3min) of inner cladding region 3. In some embodimentsouter cladding region 4 has relative refractive index greater than thatof first inner cladding region 2, thereby forming a region which is an“updoped” outer cladding region 4 with respect to first inner claddingregion 2, e.g. by adding an amount of dopant (such as germania orchlorine) sufficient to increase the relative refractive index of theouter cladding region 4. Note, however, that it is not critical that theouter cladding region 4 be updoped in the sense that an index increasingdopant must be included in the outer cladding region 4. Indeed, theraised index effect in outer cladding region 4 may be achieved bydowndoping first inner cladding region 2 with respect to outer claddingregion 4. According to some embodiments outer cladding region 4comprises a higher relative refractive index than first inner claddingregion 2, and may comprises relative refractive index delta percent Δ₄which is greater than 0.01%, and in some embodiments be greater than0.02% or 0.03%, relative to refractive index in the first inner claddingregion 2. Preferably, the higher index portion of outer cladding region4 (compared to first inner cladding region 2 (or to Δ_(3max)) extends atleast to the point where the optical power which would be transmittedthrough the optical fiber is greater than or equal to 90% of the opticalpower transmitted, more preferably to the point where the optical powerwhich would be transmitted through the optical fiber is greater than orequal to 95% of the optical power transmitted, and most preferably tothe point where the optical power which would be transmitted through theoptical fiber is greater than or equal to 98% of the optical powertransmitted. In many embodiments, this is achieved by having the“updoped” third annular region extend at least to a radial point ofabout 30 microns. Consequently, the volume V₄ of the third annularregion 4, is defined herein being calculated between radius r₃ and r₃₀(the radius at 30 microns) and thus is defined in equation 9 as

$\begin{matrix}{V_{4} = {2{\int_{r\; 3}^{r\; 30}{{\Delta_{({4 - 2})}(r)}r\ {\mathbb{d}r}}}}} & \left( {{Eq}.\mspace{14mu} 9} \right)\end{matrix}$where Δ₍₄₋₂₎ is the index difference of (Δ₄−Δ₂).

The volume V₄ of the outer cladding region 4 (inside 30 microns)compared to that of the first inner cladding region 2, is preferablygreater than 5 Δ % microns², more preferably greater than 7 Δ %microns², and may be greater than 10% Δmicrons². This volume V₄ of theouter cladding region (inside 30 microns) is in some embodiments lessthan 50% Δmicrons².

In some embodiments, the relative refractive index Δ₄ of the outercladding region 4 is greater than first inner cladding index Δ₂ by0.01%, more preferably greater than 0.02%. In some embodiments, theouter cladding region 4 comprises chlorine (Cl). In some embodiments theouter cladding region includes Germania.

The core region 1 preferably has a positive relative refractive indexthroughout, and a maximum relative refractive index Δ_(1MAX) occursbetween r=0 and r=3 microns. Δ_(1MAX) is preferably between 0.30 to0.48%, and even more preferably between 0.3 to 0.45%.

The first inner cladding region 2 preferably has a substantiallyconstant relative refractive index profile, i.e. the difference betweenthe relative refractive index at any two radii within the intermediateregion is less than 0.02%, and in some preferred embodiments less than0.01%. Thus, the relative refractive index profile of the first innercladding region 2 preferably has a substantially flat shape. In someembodiments the outer cladding region 4 is updoped relative to puresilica and in some embodiments the first inner cladding region 2 isdowndoped relative to pure silica.

The central core region 1 may comprise a alpha (α) shape, where the corealpha, α_(c), is between 1.5 and 2.5, for example 1.8<α_(c)<2.2. In somepreferred embodiments, r₁ is less than 8.0 microns, and more preferablyis between 3.5 microns and 7.0 microns. The fibers are capable ofexhibiting mode field diameter at 1310 nm between 8.2 and 9.6 microns,have a zero dispersion wavelength between 1300 and 1324 nm, a cablecutoff less than or equal to 1260 nm, and a bend loss of less than 1dB/turn when wound upon on a 10 mm radius mandrel.

In some embodiments the graded index central core region 1 comprises Gedoped silica, with Ge levels dropping as the core radius approachesouter radius r=r₁. However, in some embodiments the graded index centralcore comprises fluorine doped silica and is essentially free ofgermania. In these embodiments the cladding is either downdoped,relative to the central core region with downdopants such as F, B, ormay contain non-periodic holes or voids. In some embodiments, thedepressed-index annular portion comprises voids, either non-periodicallydisposed, or periodically disposed, or both. By “non-periodicallydisposed” or “non-periodic distribution”, we mean that when one takes across section (such as a cross section perpendicular to the longitudinalaxis) of the optical fiber, the non-periodically disposed voids arerandomly or non-periodically distributed across a portion of the fiber.Similar cross sections taken at different points along the length of thefiber will reveal different cross-sectional hole patterns, i.e., variouscross sections will have different hole patterns, wherein thedistributions of voids and sizes of voids do not match. That is, thevoids are non-periodic, i.e., they are not periodically disposed withinthe fiber structure. These voids are stretched (elongated) along thelength (i.e. parallel to the longitudinal axis) of the optical fiber,but do not extend the entire length of the entire fiber for typicallengths of transmission fiber. The voids can contain one or more gases,such as argon, nitrogen, krypton, CO₂, SO₂, or oxygen, or the voids cancontain a vacuum with substantially no gas; regardless of the presenceor absence of any gas, the refractive index in the annular portion 50 islowered due to the presence of the voids. While not wishing to be boundby theory, it is believed that the voids extend less than a few meters,and in many cases less than 1 meter along the length of the fiber.Optical fibers disclosed herein can be made by methods which utilizepreform consolidation conditions which are effective to result in asignificant amount of gases being trapped in the consolidated glassblank, thereby causing the formation of voids in the consolidated glassoptical fiber preform. Rather than taking steps to remove these voids,the resultant preform is used to form an optical fiber with voids, orvoids, therein. As used herein, the diameter of a hole is the longestline segment whose endpoints are disposed on the silica internal surfacedefining the hole when the optical fiber is viewed in perpendicularcross-section transverse to the longitudinal axis of the fiber.

In some exemplary embodiments the graded index core region 1 alsoincludes at least one alkali metal oxide dopant, for example, where inthe alkali is K (potassium), Na (sodium), Li (lithium), Cs (cesium),and, Rb (rubidium). In some exemplary embodiments the core 1 containsK₂O in the amounts of 20 ppm to 1000 ppm by weight % of K, morepreferably between 50-500 ppm wt % of K, and most preferably between50-300 ppm wt % of K. The fiber may also include chlorine. It ispreferable that the amount of chlorine is less than 1500 ppm by wt % inthe core region 1, and less than 500 ppm by wt % in the cladding regions2-4. In some embodiments, the alkali doped fiber comprises a core and/orcladding that is germania free silica (preferably less than 1% germaniaby weight, more preferably less than 0.1% germania by weight). It isnoted that the term “ppm”, unless otherwise specially noted otherwise,refers to parts per million by weight, or ppm by weight, and ameasurement in wt % can be converted to ppm by multiplying by a factorof 10,000.

The fibers disclosed herein may be drawn from optical fiber preformsmade using conventional manufacturing techniques and using known fiberdraw methods and apparatus, for example as is disclosed in U.S. Pat. No.7,565,820, the specification of which is hereby incorporated byreference.

Various exemplary embodiments will be further clarified by the followingexamples. It will be apparent to those skilled in the art that variousmodifications and variations can be made without departing from thespirit or scope of the claims.

Fiber Examples 1-25 and Comparative Example

Tables 1-4 below list characteristics of modeled illustrative fiberexamples 1-25 and comparative example. In particular, set forth belowfor each example of Tables 1-4 is the relative refractive index deltaΔ₁, alpha_(core), and outer radius r₁ of the central core region 1,relative refractive index delta Δ₂ and outer radius r₂ first innercladding region 2, r₁/r₂, relative refractive index delta Δ₃ andΔ_(3min), moat alpha (alpha_(t)), radial locations r_(3a) and r₃,(r_(3a)−r₂)/(r₃−r₂), moat volume V_(3a3) and moat volume ratioV_(3a3ratio) of the second inner cladding region 3, relative refractiveindex delta Δ₄ and volume V₄ of the outer cladding region 4, which iscalculated between inner radius r₃ of outer cladding region 3 and aradial distance of 30 microns. Also set forth (Tables 1-4) are modeleddata including: LP11 cutoff wavelength in nm, chromatic dispersion anddispersion slope at 1310 nm, chromatic dispersion and dispersion slopeat 1550 nm, mode field diameter at 1310 nm and 1550 nm, pin arraymacrobend at 1550 nm, LLWM microbend at 1550 nm in dB/m), zerodispersion wavelength (lambda0), 22 m cable cutoff, 1×10 mm, 1×20 mm and1×30 mm diameter induced bend loss in dB per turn at 1550 nm, MACCab(MFD in microns at 1310 nm/Cable Cutoff in microns).

TABLE 1 Parameter Ex-1 Ex-2 Ex-3 Ex-4 Ex-5 Ex-6 Ex-7 Ex-8 R1 (microns)5.0 5.0 6.0 6.0 5.0 5.0 6.0 6.0 Δ1_(max) (%) 0.38 0.38 0.38 0.38 0.400.40 0.40 0.40 core alpha 2 2 2 2 2 2 2 2 R2 (microns) 5.0 6.0 6.0 7.05.0 6.0 6.0 7.0 Δ2 (%) 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 R1/R21.00 0.83 1.00 0.86 1.00 0.83 1.00 0.86 R3a (microns) 17.0 17.0 17.017.0 17.0 17.0 17.0 17.0 Δ3_(min) (%) −0.45 −0.45 −0.45 −0.45 −0.45−0.45 −0.45 −0.45 moat alpha (alpha_(t)) 1 1 1 1 1 1 1 1 R3 (microns)17.0 17.0 17.0 17.0 17.0 17.0 17.0 17.0 Δ3a (%) −0.45 −0.45 −0.45 −0.45−0.45 −0.45 −0.45 −0.45 (R3a-R2)/(R3-R2) 1.00 1.00 1.00 1.00 1.00 1.001.00 1.00 Moat Volume, V_(3a3) 70 66 66 61 70 66 66 61 (% Δ microns²)Moat Volume Ratio 0.59 0.58 0.58 0.56 0.59 0.58 0.58 0.56 R4 (microns)62.5 62.5 62.5 62.5 62.5 62.5 62.5 62.5 Δ4 (%) 0.00 0.00 0.00 0.00 0.000.00 0.00 0.00 V4 (% Δ microns²) 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 MFD at1310 nm 8.70 8.86 9.23 9.33 8.57 8.71 9.09 9.19 (microns) MFD at 1550 nm9.85 10.07 10.28 10.45 9.69 9.89 10.13 10.27 (microns) LP11 Cutoff (nm)1033 1042 1219 1238 1052 1069 1252 1271 Dispersion at 1310 −0.41 −0.851.01 0.65 −0.50 −0.96 0.95 0.60 nm (ps/nm/km) Slope at 1310 nm 0.0920.092 0.093 0.093 0.092 0.092 0.093 0.093 (ps/nm2/km) Dispersion at 155017.5 17.5 19.3 18.9 17.6 17.3 19.2 18.9 nm (ps/nm/km) Slope at 1550 nm0.064 0.065 0.064 0.064 0.064 0.065 0.064 0.064 (ps/nm2/km) Cable Cutoff(nm) 1167 1150 1371 1357 1190 1179 1405 1391 MACCab (MFD in 7.46 7.716.73 6.88 7.20 7.39 6.47 6.61 microns at 1310 nm/Cable Cutoff inmicrons) 10 mm diameter 0.372 0.499 0.087 0.126 0.198 0.271 0.054 0.078Bend (dB/turn) 20 mm diameter 0.130 0.172 0.021 0.030 0.061 0.082 0.0120.017 Bend (dB/turn) 30 mm diameter 0.016 0.0192 0.0015 0.0018 0.00670.0079 0.0007 0.0009 Bend (dB/turn) Lambda0 (nm) 1314 1319 1299 13031315 1320 1300 1304 LLWM (dB/m at 1550 0.605 0.64 0.2794 0.308 0.4240.45 0.174 0.192 nm) Pin Array (dB at 1550 28.10 26.60 6.34 6.29 18.3217.48 3.60 3.58 nm)

TABLE 2 Parameter Ex-9 Ex-10 Ex-11 Ex-12 Ex-13 Ex-14 Ex-15 Ex-16 R1(microns) 5.4 5.4 5.4 5.4 6.08 5.68 5.68 5.68 Δ1_(max) (%) 0.40 0.400.42 0.42 0.40 0.40 0.40 0.40 core alpha 2 2 2 2 2 2 2 2 R2 (microns)5.4 6.6 5.4 6.6 9.12 8.52 8.52 5.68 Δ2 (%) 0.00 0.00 0.00 0.00 0.00 0.000.00 0.00 R1/R2 1.00 0.82 1.00 0.82 0.67 0.67 0.67 1.00 R3a (microns)16.8 16.8 16.8 16.8 15.26 14.2 15.27 14.27 Δ3_(min) (%) −0.45 −0.45−0.43 −0.43 −0.20 −0.20 −0.10 −0.10 moat alpha (alpha_(t)) 1 1 1 1 1 1 11 R3 (microns) 16.8 16.8 16.8 16.8 15.26 14.20 15.27 14.27 Δ3a (%) −0.45−0.45 −0.43 −0.43 −0.20 −0.20 −0.10 −0.10 (R3a-R2)/(R3-R2) 1.00 1.001.00 1.00 1.00 1.00 1.00 1.00 Moat Volume, V_(3a3) 66 62 72 68 16.2 14.17.1 9.7 (% Δ microns²) Moat Volume Ratio 0.58 0.57 0.63 0.63 0.54 0.550.44 0.57 R4 (microns) 62.5 62.5 62.5 62.5 62.5 62.5 62.5 62.5 Δ4 (%)0.00 0.00 0.02 0.02 0.00 0.00 0.00 0.00 V4 (% Δ microns²) 0.0 0.0 12.412.4 0.0 0.0 0.0 0.0 MFD at 1310 nm 8.82 8.96 8.74 8.85 9.29 9.10 9.119.04 (microns) MFD at 1550 nm 9.90 10.13 9.79 9.97 10.49 10.34 10.3910.25 (microns) LP11 Cutoff (nm) 1123 1146 1078 1093 1339 1252 1265 1240Dispersion at 1310 0.18 −0.29 0.34 −0.10 0.06 −0.05 −0.69 −0.32 nm(ps/nm/km) Slope at 1310 nm 0.092 0.0925 0.035 0.036 −0.019 0.071 0.0830.081 (ps/nm2/km) Dispersion at 1550 18.4 18.0 18.4 18.1 17.9 17.3 16.917.3 nm (ps/nm/km) Slope at 1550 nm 0.0640 0.0647 0.063 0.063 0.0620.063 0.061 0.061 (ps/nm2/km) Cable Cutoff (nm) 1274 1261 1229 1217 12891192 1173 1180 MACCab (MFD in 6.92 7.10 7.11 7.27 7.21 7.63 7.77 7.66microns at 1310 nm/Cable Cutoff in microns) 10 mm diameter 0.12 0.170.07 0.09 1.65 3.23 5.42 4.47 Bend (dB/turn) 20 mm diameter 0.032 0.0440.017 0.023 0.31 0.67 1.11 0.92 Bend (dB/turn) 30 mm diameter 0.0020.003 0.002 0.002 0.003 0.008 0.010 0.009 Bend (dB/turn) Lambda0 (nm)1308 1313 1301 1313 1313 1317 1318 1314 LLWM (dB/m at 1550 0.309 0.3380.122 0.148 0.231 0.211 0.224 0.193 nm) Pin Array (dB at 1550 10.14 9.7516.77 16.39 4.38 8.34 9.16 9.2 nm)

TABLE 3 Parameter Ex-17 Ex-18 Ex-19 Ex-20 Ex-21 Ex-22 Ex-23 Ex-24 Ex-25R1 (microns) 5.4 5.6 5.6 5.6 5.2 5.68 5.68 6.16 6.56 Δ1_(max) (%) 0.400.40 0.40 0.40 0.40 0.40 0.40 0.42 0.44 core alpha 2 2 2 2 3 2 2 1.5 1R2 (microns) 5.4 7.0 7.0 7.0 6.5 8.52 8.52 6.16 6.6 Δ2 (%) 0.00 0.000.00 0.00 0.00 0.00 0.00 0.00 0.00 R1/R2 1.00 0.80 0.80 0.80 0.80 0.670.67 1.00 1.00 R3a 16.8 17.4 17.4 17.4 17.4 14.20 14.20 15.46 16.47(microns) Δ3_(min) (%) −0.45 −0.20 −0.10 −0.10 −0.10 −0.20 −0.10 −0.20−0.20 moat alpha 0.5 2 2 5 2 1 1 1 1 (alpha_(t)) R3 (microns) 16.8 17.417.4 17.4 17.4 15.62 18.46 15.46 16.47 Δ3a (%) −0.45 −0.20 −0.10 −0.10−0.10 −0.20 −0.10 −0.20 −0.20 (R3a-R2)/ 1.00 1.00 1.00 1.00 1.00 0.800.57 1.00 1.00 (R3-R2) Moat Volume, 46 37.3 18.6 22.3 16.1 22.2 20.822.9 26.0 V_(3a3) (% Δ microns²) Moat Volume 0.40 0.73 0.73 0.88 0.620.65 0.78 0.57 0.57 Ratio R4 (microns) 62.5 62.5 62.5 62.5 62.5 62.562.5 62.5 62.5 Δ4 (%) 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 V4 (%Δ 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 microns²) MFD at 1310 8.84 9.009.04 9.00 8.79 9.09 9.11 9.15 9.15 nm (microns) MFD at 1550 10 10.1710.29 10.2 9.92 10.36 10.36 10.33 10.43 nm (microns) LP11 Cutoff 11621216 1231 1218 1264 1268 1260 1245 1239 (nm) Dispersion at −0.35 −0.23−0.59 −0.31 −0.04 −0.50 −0.67 −0.15 −1.02 1310 nm (ps/nm/km) Slope at0.067 0.025 0.076 0.065 0.067 0.072 0.076 0.042 0.073 1310 nm(ps/nm2/km) Dispersion at 17.6 17.8 17.1 17.5 17.8 17.5 17.0 18.0 17.41550 nm (ps/nm/km) Slope at 0.063 0.063 0.062 0.062 0.061 0.063 0.0620.063 0.065 1550 nm (ps/nm2/km) Cable Cutoff 1218 1238 1186 1196 12141231 1227 1244 1246 (nm) MACCab 7.26 7.27 7.62 7.52 7.24 7.38 7.42 7.357.34 (MFD in microns at 1310 nm/Cable Cutoff in microns) 10 mm 0.47 0.662.63 2.00 1.73 1.78 1.97 1.59 1.31 diameter Bend (dB/turn) 20 mm 0.0110.015 0.056 0.043 0.033 0.037 0.041 0.033 0.028 diameter Bend (dB/turn)30 mm 0.0045 0.004 0.008 0.007 0.004 0.006 0.006 0.005 0.005 diameterBend (dB/turn) Lambda0 1315 1319 1318 1315 1311 1317 1319 1314 1324 (nm)LLWM (dB/m 0.153 0.185 0.209 0.189 0.148 0.208 0.223 0.203 0.231 at 1550nm) Pin Array (dB 9.81 7.36 9.08 8.78 4.32 6.58 7.75 7.88 8.74 at 1550nm)

TABLE 4 Comparative Parameter Example R1 (microns) 4.5 Δ1_(max) (%) 0.34core alpha 20.0 R2 (microns) 4.5 Δ2 (%) 0.0 R1/R2 1.00 R3a (microns) notapplicable Δ3_(min) (%) not applicable moat alpha (alpha_(t)) notapplicable R3 (microns) not applicable Δ3 (%) not applicable (R3a −R2)/(R3 − R2) 0.00 Moat Volume, V_(3a3) (% Δ microns²) 0.00 Moat VolumeRatio not applicable R4 (microns) 62.5 Δ4 (%) 0.00 MFD at 1310 nm(microns) 9.18 MFD at 1550 nm (microns) 10.40 LP11 Cutoff (nm) 1327Dispersion at 1310 nm 0.17 (ps/nm/km) Slope at 1310 nm (ps/nm²/km) 0.086Dispersion at 1550 nm 17.0 (ps/nm/km) Slope at 1550 nm (ps/nm²/km) 0.058Cable Cutoff (nm) 1177 MACCab (MFD in microns at 7.8 1310 nm/CableCutoff in microns) 10 mm diameter Bend (dB/turn) 8.66 20 mm diameterBend (dB/turn) 0.49 30 mm diameter Bend (dB/turn) 0.012 Lambda0 (nm)1308 LLWM (dB/m at 1550 nm) 0.549 Pin Array (dB at 1550 nm) 9.16

The exemplary fibers 1-25 of Tables 1-4 have dispersion at 1310 nm ofabout −1.05 ps/nm/km to about 1 ps/nm/km, LP11 cut-off wavelengthbetween about 1025 nm and 1300 nm, and a bend loss of less than 5.5dB/turn around a 10 mm diameter mandrel at 1550 nm wavelength. Theexemplary embodiments fibers 1-25 have profile designs having a gradedindex central core region 1 having outer radius r₁, having a relativerefractive index Δ₁, a maximum relative refractive index Δ_(1max) andhaving an alpha profile, alpha_(core), of 0.5≦alpha_(core)≦4; and aninner cladding region 3 (i.e., the trench) surrounding the graded indexcentral core region and comprising a relative refractive index delta Δ₃that becomes more negative with increasing radius. The inner claddingregion 3 has an inner radius r₂, an outer radius r₃>10 microns, and aminimum relative refractive index Δ_(3min) such that Δ_(1max)>Δ_(3min),r₃≧r_(3a), and 0.5≦(r_(3a)−r₂)/(r₃−r₂)≦1, where r_(3a) is a distancefrom fiber centerline where Δ₃ first reaches the value Δ_(3min). Theinner cladding region 3 has an alpha profile, alpha_(s) such that0.5≦alpha_(t)≦5. The outer cladding region surrounds the inner claddingregion and has a relative refractive index Δ₄, and Δ_(3min)<Δ₄. In theseembodiments the absolute difference between (Δ₄−Δ_(3min)) is0.08%≦|Δ₄−Δ_(3min)|≦0.7% and the absolute difference between Δ_(3min)and Δ₂ is greater than 0.03%. The absolute value V_(3a3) of the secondinner cladding region is 5% Δmicrons²≦V_(3a3)≦105% Δmicrons², and themoat volume ratio is 0.3≦V_(3a3ratio)≦0.8. The above fibers 1-25 ofTables 1-4 exhibit a 22 m cable cutoff less than or equal to 1400 nm andin many embodiments less than or equal to 1260 nm, a mode field diameter(MFD) at 1310 nm between 8.2 and 9.6 microns and have a zero dispersionwavelength λo and 1300 nm≦λo≦1324 nm.

More specifically, preferably, exemplary optical fiber embodiments 10described herein exhibit a bend loss at 1550 nm, when wound upon on a 15mm diameter mandrel, of less than 0.5 dB/turn, and in some cases lessthan 0.25 dB/turn. These fibers also exhibit a bend loss at 1550 nm,when wound upon on a 10 mm diameter mandrel, of less than 1 dB/turn,more preferably less than 0.5 dB/turn, and some fibers most preferablyless than 0.2 dB/turn. The fibers exhibit a bend loss at 1550 nm, whenwound upon on a 15 mm diameter mandrel, of less than 0.25 dB/turn, andsome fibers more preferably less than 0.15 dB/turn. The fibers exhibit abend loss at 1550 nm, when wound upon on a 20 mm diameter mandrel, ofless than 0.1 dB/turn, and some fibers more preferably less than 0.03dB/turn. Some of the above fibers exhibit a bend loss of less than 0.75dB/turn when wound upon on a 20 mm radius mandrel and exhibits a MACCabnumber between 6.4 and 8.5. (Note, MACCab number=MFD in microns at 1310nm/Cable Cutoff in microns.) These fibers also exhibit a bend loss at1550 nm, when wound upon on a 30 mm diameter mandrel, of less than 0.01dB/turn, and some fibers more preferably less than 0.003 dB/turn. Someof these examples employ chlorine in the outer cladding region in anamount greater than 2000 ppm, and in some cases greater than 3000 oreven greater than 4000 ppm by weight. In some embodiments the outercladding region comprises chlorine in an amount greater than 2000 andless than 12000 ppm by weight.

Attenuation (spectral) at 1550 nm is preferably less than 0.21 dB/km,more preferably less than 0.20 dB/km, even more preferably less than0.197 dB/km. In some preferred embodiments the attenuation (spectral) at1550 nm is less than or equal to 0.191 dB/km, even more preferably lessthan or equal to 0.189 dB/km, even more preferably less than or equal to0.182 dB/km.

Thus, the embodiments of the optical fibers 10 described herein provideoutstanding bending performance, and additionally provide cutoffwavelengths suitable for single mode operation at wavelengths greaterthan about 1260 nm.

In some embodiments, the core region 1 may comprise a relativerefractive index profile having a so-called centerline dip which mayoccur as a result of one or more optical fiber manufacturing techniques.However, the centerline dip in any of the relative refractive indexprofiles disclosed herein is optional.

The optical fiber 10 disclosed herein comprises a core and a claddinglayer (or cladding or outermost annular cladding region) surrounding thecore. Preferably, the core is comprised of silica doped with germanium,i.e. germania doped silica. Dopants other than germanium, singly or incombination, may be employed within the core, and particularly at ornear the centerline, of the optical fiber disclosed herein to obtain thedesired relative refractive index and density.

Preferably, the optical fiber disclosed herein has a silica-based coreregion 1 and cladding. In preferred embodiments, the cladding has anouter diameter, 2 times r₄, of about 125 micron.

The fibers disclosed herein exhibit low PMD values particularly whenfabricated with OVD processes. Spinning of the optical fiber may alsolower PMD values for the fiber disclosed herein.

It is to be understood that the foregoing description is exemplary onlyand is intended to provide an overview for the understanding of thenature and character of the fibers which are defined by the claims. Theaccompanying drawings are included to provide a further understanding ofthe preferred embodiments and are incorporated and constitute part ofthis specification. The drawings illustrate various features andembodiments which, together with their description, serve to explain theprincipals and operation. It will become apparent to those skilled inthe art that various modifications to the preferred embodiments asdescribed herein can be made without departing from the spirit or scopeof the appended claims.

What is claimed is:
 1. A single mode optical fiber comprising: a gradedindex central core region having outer radius r₁, having a relativerefractive index Δ₁, a maximum relative refractive index Δ_(1max) andhaving an alpha profile, alpha_(core), of 0.5≦alpha_(core)≦4; a claddingregion including (a) a trench region surrounding said graded indexcentral core region and comprising a relative refractive index delta Δ₃profile that becomes more negative with increasing radius, said trenchregion having an inner radius r₂, an outer radius r₃>10 microns, and aminimum relative refractive index Δ_(3min) such that Δ_(1max)>Δ_(3min),r₃≧r_(3a), and 0.5≦(r_(3a)−r₂)/(r₃−r₂)≦1, where r_(3a) is a distancefrom fiber centerline where Δ₃ first reaches the value Δ_(3min), saidtrench region having an alpha profile, alpha_(t) such that0.5≦alpha_(t)≦5, and (b) an outer cladding region surrounding saidtrench region and having a relative refractive index Δ₄, andΔ_(3min)<Δ₄, and wherein 0.08%≦|Δ₄−Δ_(3min)|≦0.7% and the absolutedifference between Δ_(3min) and Δ₂ is greater than 0.03, the absolutevalue V_(3a3) of the trench region is 5% Δmicrons²≦V_(3a3)≦105%Δmicrons², and said fiber exhibits a 22 m cable cutoff less than orequal to 1400 nm.
 2. A single mode optical fiber comprising: a gradedindex central core region having outer radius r₁, having a relativerefractive index Δ₁, a maximum relative refractive index Δ_(1max) andhaving an alpha profile alpha_(core), of 0.5≦alpha_(core)≦4; a claddingregion including (a) a trench region surrounding said graded indexcentral core region and comprising a relative refractive index delta Δ₃profile that becomes more negative with increasing radius, said trenchregion having an inner radius r₂, an outer radius r₃>10 microns, and aminimum relative refractive index Δ_(3min) such that Δ_(1max)>Δ_(3min),r₃≧r_(3a), and 0.5≦(r_(3a)−r₂)/(r₃−r₂)≦1, where r_(3a) is a distancefrom fiber centerline where Δ₃ first reaches the value Δ_(3min), saidtrench region having an alpha profile, alpha_(t) such that0.5≦alpha_(t)≦5, and (b) an outer cladding region surrounding saidtrench region and having a relative refractive index Δ₄, andΔ_(3min)<Δ₄, wherein the cladding region further comprises a first innercladding region that has a relative refractive index delta Δ₂ and issituated between said central core region and said trench region, suchthat the outer radius of said first inner cladding region equals to theinner radius r₂ of said trench region, and r₂≦10 microns, and0.65≦r₁/r₂<1, said first inner cladding region having a relativerefractive index Δ₂; and Δ_(1max)>Δ₂>Δ_(3min), and0.08%≦|Δ₄−Δ_(3min)|≦0.7%, the absolute difference between Δ₃Δ₂ isgreater than 0.03, the absolute value V_(3a3) of the trench region is 5%Δmicrons²≦V_(3a3)≦105% Δmicrons², and said fiber exhibits a 22 m cablecutoff wavelength of less than or equal to 1400 nm.
 3. The optical fiberof claim 1 wherein 0.3%<Δ_(1max)<0.48%.
 4. The optical fiber of claim 2wherein 0.08%≦|Δ₄−Δ_(3min)|≦0.25%.
 5. The optical fiber of claim 2wherein 0.25%≦|Δ₄−Δ_(3min)|≦0.55%.
 6. The optical fiber of claim 2wherein the graded index central core region comprises germania dopedsilica.
 7. The optical fiber of claim 2, wherein the graded indexcentral core comprises fluorine doped silica and is essentially free ofgermania.
 8. The optical fiber of claim 7, wherein the graded indexcentral core region comprises potassium.
 9. The optical fiber of claim2, wherein the first inner cladding region is essentially free offluorine and germania.
 10. The optical fiber of claim 2, wherein Δ₄>Δ₂for a radial length extending from r₃ to a radius of at least 30microns.
 11. The optical fiber of claim 2, wherein the profile volume,V₄ of the outer cladding region, calculated between the outer radius oftrench region and a radial distance of 30 microns, is equal to:V₄ = 2∫_(r 3)^(r 30)Δ⁽⁴ ⁻ ²⁾(r)r 𝕕r and |V₄| is at least 5% Δmicrons².12. The optical fiber of claim 2, wherein said fiber exhibits a bendloss of less than 0.75 dB/turn when wound upon on a 20 mm radius mandreland exhibits a MACCab number between 6.4 and 8.5.
 13. The optical fiberof claim 2, wherein the width of trench region r₃−r₂ is between 3 and 20microns.
 14. The optical fiber of claim 2, wherein said fiber exhibits abend loss of less than 1 dB/turn when wound upon on a 10 mm diametermandrel.
 15. The optical fiber of claim 2, where α_(t) is 5≧α_(t)≧0.5.16. The optical fiber of claim 2 wherein 0.01%≦|Δ₄−Δ₂|.
 17. The opticalfiber of claim 2 having a moat volume ratio of 0.3≦V_(3a3ratio)≦0.8. 18.The optical fiber of claim 2, wherein said trench region has a volumeV_(3a3) and 5 Δ % microns²≦V_(3a3)≦105 Δ % microns².
 19. The opticalfiber of claim 2 having a 22 m cable cutoff less than or equal to 1260nm, and has a zero dispersion wavelength λo of 1300 nm≦λo≦1324 nm.
 20. Asingle mode optical fiber comprising: a graded index central core regionhaving outer radius r₁, having a relative refractive index Δ₁, a maximumrefractive index Δ_(1max) and having an alpha profile, alpha_(core), of0.5≦alpha_(core)≦4; a cladding region comprising (i) a first innercladding region having an outer radius r₂≦10 microns and relativerefractive index Δ₂ and 0.65≦r₁/r₂≦1; (ii) and a second inner claddingregion having an outer radius r₃>10 microns and comprising a relativerefractive index Δ₃ and a minimum relative refractive index Δ_(3min),wherein said second inner cladding region has a relative refractiveindex delta that becomes more negative with increasing radius, whereinsaid second cladding region has an alpha profile, alpha_(t), of0.5≦alpha_(t)≦5; and (iii) an outer cladding region surrounding thesecond inner cladding region and comprising relative refractive indexΔ₄, wherein Δ_(1max)>Δ₂>Δ_(3min), and Δ_(3min)<Δ₄; and wherein0.5≦(r_(3a)−r₂)/(r₃−r₂)≦1 where r_(3a) is a distance from fibercenterline where Δ₃ first reaches the value Δ_(3min), and said fiberexhibits a 22 m cable cutoff wavelength of less than or equal to 1400nm.